currently proposed spectrally efficient radio systems such as the proposed European standard for digital trunked radios require highly linear power amplifiers to minimize the transmission of modulation products or "splatter" on adjacent channels. A technique for achieving the necessary linearity performance in power amplifiers involves the use of a linearization training sequence such as is described in U.S. Pat. No. 5066923 of Motorola Inc.
A problem with this method of linearizing of power amplifiers is that a finite amount of time needs to be allocated for the training sequence to be transmitted. In time division multiple access systems, the allocating of a finite amount of air time for training is a particularly costly overhead which reduces overall system throughput.
One method for avoiding the need to allocate excessive air time for training is described in UK patent application No. 9204496.5 of Motorola Limited. In the arrangement described in that patent application, training is achieved off-air by use of a circulator and an antenna switch and a load, in which the training sequence is transmitted into the load by selective operation of the antenna switch.
There is a perceived need in the art for a manner of achieving linearization of the power amplifier without the use of substantial additional hardware and with a minimum of air time being allocated for training. Other requirements that need to be addressed are a minimum delay between a requirement to transmit and the achievement of linearity prior to transmission and/or the minimisation of transmissions while not fully linearized to an acceptably low percentage of all transmissions.